1. Field of the Invention
The present invention relates to a thick film circuit board and to a method of producing the same. More specifically, the invention relates to a thick film circuit board that can be produced at a low cost, to a method of producing the same and to an integrated circuit device using the thick film circuit board.
2. Description of the Related Art
In the thick film circuit board in a hybrid integrated circuit device, conducting layers of an electric circuit are formed on both surfaces of an insulating base member in order to decrease the size. The conducting layers formed on both surfaces of the base member are made of a conductor formed depending upon a predetermined circuit pattern. The conducting layers formed on both surfaces of the base member are electrically connected together through conducting portions that maintain electric conduction in through holes formed penetrating through the base member.
The conducting layers and the conducting portions are made of a silver-containing conductor or a copper-containing conductor. The conductors are formed by firing an alloy material on the surfaces of the base member (see Japanese Unexamined Patent Publications (Kokai) Nos. 11-177016 and 2000-312062).
The silver-containing conductor easily develops electro-migration and has a problem concerning the reliability. Therefore, a silver-containing conductor to which palladium is added has been devised accompanied, however, by a problem of low electric conduction.
Further, since copper by itself tends to be easily oxidized, the atmosphere must be controlled when the copper-containing conductor is to be fired, thus driving up the cost. The atmosphere must be controlled even when a resistor is to be fired in the circuit pattern. Therefore, a limitation is imposed on the material for forming the resistor, also driving up the cost. As the copper-containing conductors, there have been known high-temperature fired copper that is fired at 800 to 900° C. and low-temperature fired copper that is fired at 600 to 700° C.